Gliederung

Introduction: The determination of the origin of chronic foot OA pain is challenging since clinical examination of the foot faces a complex anatomy with several joints, osseous, and non-osseous structures contributing to the symptoms. Non-invasive imaging methods like plain radiography, CT or MRI show poor correlation of degenerative signs with pain degree. Functional imaging based on the detection of activated osteoblasts with 99mTc-Dicarboxypropandiphosphate (DPD) shows promising results for localization of painful facet joints in the lower spine, but so far no evaluation for chronic OA pain conditions in foot joints has been conducted. Additionally, the diagnostic potential of scintigraphy is limited due to poor spatial resolution. Single Photon Emission Computed Tomography - Computed Tomography (SPECT-CT) is a new hybrid technique allowing perfect overlay of functional and anatomical images. We hypothesised that diagnostic infiltration with a local anaesthetic of a painful hindfoot or midfoot joint showing 99mTc-DPD-uptake as indicated by SPECT-CT, leads to a positive OA pain response.

Methods: 26 patients with chronic OA pain and radiological signs of OA in a hindfoot or midfoot joint (27 feet) were included. Plain radiography was performed to detect degenerative changes and to rule out pathologies different from OA. Pain status was measured by Visual Analogue Scale (VAS). AOFAS hindfoot/midfoot score and SF-36-score were documented. All patients received a 99mTc-DPD SPECT-CT (Symbia T2, Siemens). The localisation of 99mTc-DPD-uptake and consequently the site of infiltration were defined. The infiltration was performed with a local anaesthetic (bupivacaine) and iodine solution under CT-guidance with exact documentation of the contrast media deposit by CT. Pain status was assessed directly post-infiltration. Pain relief in responders was defined as reduction of VAS-score 50% immediately after infiltration, partial response as reduction of 50%.

Results: Infiltration was performed in 26 hindfoot joints and 5 midfoot as indicated by 99mTc-DPD-uptake in SPECT-CT. Subsequent CT control scans showing contrast media depot confirmed exact successful infiltration in all indicated joints. In 22 patients an immediate significant (p0.01) postinterventional pain reduction of VAS more than 50% was observed. Mean VAS before infiltration was 5.77 (range 2-10; SD 2.22 ) and 0.82 (range 0-4; SD 1.26) immediately after infiltration. Two patients showed a partial response and two patients showed no pain resolution after infiltration.

Conclusion: The results show a significant correlation of uptake and pain resolution after infiltration allowing precise identification of OA hindfoot joints as pain inducing foci. Non-invasive SPECT-CT offers good prediction of outcome after infiltration improving the localisation of the pain inducing pathology, thus aiding in pre-operative planning and avoiding unnecessary interventions.